This invention relates to a method of determining the magnesium content in molten aluminum alloys, and more particularly to a method for measuring the magnesium content in Al-Si aluminum alloy.
The magnesium content in molten aluminum, especially molten Al-Si aluminum alloys has a great influence in the strength of aluminum alloy products.
Al-7% Si-0.3% aluminum alloy which is usually utilized for making thin aluminum foil sheet contains about 0.3% by weight of magnesium in molten state. Tensile strength of the above aluminum alloy is about 28 Kg/mm2, but if the magnesium content is reduced to about 0.1% by weight , the tensile strength of this aluminum alloy decreases to about 15 Kg/mm2.
The chemical composition of the conventional aluminum alloys are standardized by JIS, ASTEM, AISI, SAE, BC, DIN, VDEh, NF, EN and ISO, and an analysis of the composition is affixed to the alloys. If the alloy is melted, the content of chemical composition other than magnesium (Mg) does not change, but the molten magnesium floats on the surface of the molten aluminum alloy magnesium and is finally oxidized so that the quantity of magnesium in the alloy will be decreased.
Usually, in order to prevent from the decrease of the content of magnesium in the aluminum alloy magnesium is added to the molten aluminum alloy.
For this purpose, however, it is necessary to measure the content of magnesium in the molten aluminum alloy before casting. To apply an emission spectrochemical analysis in order to measure the magnesium content in the aluminum alloy is very expensive and requires complicated operations.
Thus, in view of the above disadvantages, the main object of the present invention is to provide a simple method of determining the magnesium content in the molten aluminum alloys.
Another object of the invention is to provide a method for measuring the content of magnesium in aluminum alloy for the purpose to prevent deterioration of the quality of aluminum alloy products before casting.
In order to attain the above objects, a method for determining the magnesium content in molten aluminum alloy according to the present invention consists of steps of carrying out the thermal analysis of the molten alloy to obtain a cooling curve; measuring the eutectic temperature of the molten alloy from the cooling curve obtained; and determining the magnesium content in the molten aluminum alloy by using an equation prepared in advance.
According to the present invention, the molten aluminum alloy is poured into a sampling vessel which is usually used to measure a cooling curve in the thermal analysis.
A small amount, for example about 0.2 percent of weight of phosphorus (P) and/or sulphur (S) may be added into the vessel as the additive.
Further, Cu-P, Al-Cu-P and Zn-S or a mixture of these alloys may be used as the additive.